Various types of rotatably driven cutting tools are known and typically used in performing machining functions. These include twist drills, boring bars, milling cutters, screw thread taps, reamers, etc. Typically, such tools are mounted to the spindle by use of means such as three-jaw chucks or other similar apparatus. Such devices are available commercially and function to translate the rotational motion of the spindle to the tool.
Such chucks serve well to mount a tool particularly when close tolerances are not required. When close tolerances are necessary, however, they frequently prove inefficient for various reasons.
Even with a brand new chuck, an eccentricity of 0.0050 inches can be present between the tool's design axis of rotation and the axis of rotation of the driving spindle. While such eccentricity might be acceptable in some applications, it might prove grossly unacceptable in others.
This problem is further exacerbated by non-uniform wear of grasping surfaces of the jaws after periods of use. Normal wear of the rotatably driven tool grasping chuck surfaces does not proceed uniformally. Thus, axial eccentricity of a rotating cutting tool grasped and driven by the jaws of a chuck typically increases with time of use of the chuck. This is particularly true if the rotating cutting tool should slip within the grasp of the chuck jaws because they are insufficiently tightened to fully resist the torque required by the tool. After a period of time, therefore, even if the gripping jaws were perfectly machined when the chuck was new, the chuck loses its ability to receive and clamp in a precisely centered fashion the driving shank of the tool.
As can be seen, therefore, a central longitudinal axis of a tool such as a twist drill, for example, can easily become spaced at a distance from the axis of rotation of the spindle by which the tool is driven. The tool will, therefore, be made to orbit the spindle's axis of rotation. The hole drilled by such a tool will have a radius equal to the radius of the tool plus the dimension of eccentricity.
Rotary cutting tools are typically provided in certain standard sizes. On occasion, although infrequently, a machinist might be required to make a cut sized between two standard sizes. Rather than being required to obtain a specially constructed tool for this purpose, the cut can be made by rotating the next smaller sized tool eccentrically. That is, the axis of the tool can be displaced from the axis of rotation of the driving spindle by design in order to accomplish the desired cut.
Various structures have been devised to solve these problems in the prior art. For example, U.S. Pat. No. 3,088,746 (Highberg et al) illustrates a RADIALLY ADJUSTABLE CHUCK providing four set screws to forcibly displace the chuck and its grasping jaws assembly to a position at which the axis of the chuck is alligned with the axis of rotation of a driving spindle. Such structures, however, do not ensure that the axis of the tool, once adjusted by the set screws, is a precisely parallel extension of the axis of rotation. While the location of the axis might be adjusted radially, the device of Highberg et al does not provide means for ensuring that the tool's axis does not become canted relative to the rotational axis of the drive spindle. Consequently, rather than solving the problems which the device addresses, the Highberg et al structure can exaggerate them.
The present invention is a device directed to the solving of all of the problems existent in the prior art. It is an improved eccentricity adjustment device which not only adjusts the radial placement of the axis of the tool relative to the spindle's axis of rotation, but it also functions to effect parallelism between the tool's axis and the rotational axis of the spindle.